Aggregation of hydrophobic-amphiphilic block copolymers

TL;DR

This paper develops a mean-field theory to analyze the diverse morphologies formed by hydrophobic-amphiphilic block copolymers, revealing how composition and architecture influence self-assembled structures like micelles and vesicles.

Contribution

It introduces a theoretical framework predicting copolymer aggregation morphologies based on architecture and pendant size, explaining experimental observations of complex micellar structures.

Findings

Copolymers with small pendants form precipitates or void-containing aggregates.

Moderate pendants lead to lamellar structures or vesicles at low amphiphilic content.

Large polar pendants mainly form granular branched micelles.

Abstract

We analyze the aggregation of locally amphiphilic copolymers with blocky architecture and uniformly distributed amphiphilic moieties in terms of a mean-field theory. Locally amphiphilic structure is characteristic of many thermoresponsive polymers, both linear and grafted, which endows them with local surface activity. Self-assembly of such copolymers exhibits a rich diversity of morphologies, which are analyzed in the present work in the limit of high surface activity of amphiphilic dimers with solvophilic/polar pendants. Depending on the composition and architecture of the copolymer and sizes and interaction parameters of the solvophilic/polar pendants, we build morphological diagrams of copolymer solutions. Copolymers with small volume pendants form precipitates or large aggregates with internal voids containing these pendants. For moderate volume pendants, a lamellar structure (or large vesicles) is observed at smaller fractions of amphiphilic monomer units in the chain and micelles are formed at larger fractions of these units. The sizes and shapes of micelles depend on the monomer distribution along the chain, and the blocky architecture favors the existence of single spherical micelles or spherical particles that constitute compound micelles. For sufficiently large polar pendants, copolymers of both types mainly form granular branched compound micelles. The distance at which adjacent hydrophobic and polar groups are located in a chain determines the size of domains and particles formed by locally amphiphilic blocks or chains. Our predictions explain the existence of dense multicore complex micelles consisting of beads of several tens of nanometers size and other structures such as disc-shaped micelles.